1. Field of the Invention
The present invention relates to communications systems in general and in particular to fiber optic/copper wire networks whose EMI characteristics meet Federal Trade Commission (FTC) standards.
2. Prior Art
The proliferation of personal computers, word processors and other data terminal equipment (DTE) has created a need for efficient communications highways to interconnect the DTE. Historically, electrical wires have been used to interconnect the devices. The use of electrical wires is acceptable provided that the data rate is less than say twenty m bits per sec. As the data rate exceeds the allowed maximum the wires and associated connectors and panels behave like transmitters to pollute the atmosphere with an undue amount of radiation which causes radio frequency interference and other types of EMI problems. The interference problem cannot be tolerated because most national governments set EMI standards, e.g., ANSI C63.4 for communication devices. The governments usually impose severe penalties on manufacturers whose devices violate the EMI standards. In severe cases a manufacturer can be forced to withdraw violating devices from the marketplace.
To circumvent the narrow bandwidth and EMI problems, the prior art has used fiber optic media for interconnecting the devices. Even though the fiber optic media solves the radiation and bandwidth problems, it too has inherent problems which must be dealt with in order to provide an adequate interconnecting network for interconnecting DTE. In the first instance, fiber optic media is expensive and difficult to tap in order to provide the large number of drops needed in a sequential multi-station network such as the IBM.sup.R Cabling System (ICS) used to interconnect the IBM Token Ring Local Area Network (LAN). Details of the ICS and LAN are set forth in IBM Technical Interface Spec. GA27-3773-0 and ANSI Standards TR-41.8.1 (SP-1907-B). The ANSI literature covers the standard for wiring commercial buildings. Due to the high cost associated with multi-drop configuration it is more expedient to use mixed media in which fiber optic is used for the backbone network and less expensive media such as wire drops to interconnect office outlets to the fiber optic backbone network. Stated another way, the distribution network from the office wall to the distribution panel or wiring closet (WC) is wire media while the backbone network between WC is fiber optic media. Other reasons for this combination are that wire is more terminally versatile than fiber and that wire may already be installed.
The mixed media transmission (fiber and wire) solution can also be used to address problems posed by pre-wired buildings. The owners of these buildings have significant assets invested in wiring the buildings and are very reluctant in pursuing a solution which requires the complete replacement of the wire with fiber optics. A more acceptable solution is to replace the backbone network with fiber communications media and reuse the pre-wired distribution network which is already present in the buildings.
The most significant problem which mixed media network poses is EMI which occurs in the wire distribution portion of the network. Acceptance of these networks will not occur until the EMI problems are solved.
A prior art patent, U.S. Pat. No. 4,809,361, describes an optical/electrical transceiver for interconnecting terminals to an optical fiber cable. U.S. Pat. No. 4,501,021 describes an optical-electrical interface (OEI) for coupling electrical cables supporting electrical devices to global optical cables. Neither of the prior art references address high speed data transmission on copper wire and the associated EMI problems.